1. Field of the Invention
The present invention relates to a coin checker or a coin sorting apparatus for electrically determining the genuineness or spuriousness and the class of a coins used with various vending machines.
2. Description of the Prior Art
An electronic coin-sorting apparatus comprises detection coils arranged as elements of oscillators distributed along a coin passage. With the approach of a coin to a detection coil, the impedance of the detection coil changes followed by a change in the oscillation constant, that is a change in the oscillation frequency or oscillation level of the associated oscillator. The change varies with sorting factors such as the outside diameter, thickness or material of the coin. By comparing the change with reference values stored in a memory in advance for various coins, it is possible to determine the genuineness or spuriousness and the denomination or class of the respective coins.
As an example, take the case where an A coin is identified by comparing the maximum change of the oscillation frequency with a reference value. Assume that the maximum changes of the oscillation frequencies of the outside-diameter detecting oscillator, material detecting oscillator and the thickness detecting oscillator for a coin inserted in the apparatus are .DELTA.f.sub.1 max, .DELTA.F.sub.2 max, .DELTA.F.sub.3 max respectively, and the reference values stored in advance for detection of the outside diameter, material and thickness of the A coin are F.sub.1 (A), F.sub.2 (A) and F.sub.3 (A) respectively. If the inserted coin is to be identified as an A coin, it is necessary and sufficient to satisfy the three conditions specified below.
f.sub.1 (A)-.alpha..sub.A .ltoreq..DELTA.f.sub.1 max.ltoreq.f.sub.1 (A)+.alpha..sub.A'. . . for checking outside diameter PA1 f.sub.2 (A)-.beta..sub.A .ltoreq..DELTA.f.sub.2 max.ltoreq.f.sub.2 (A)+.beta..sub.A'. . . for checking material PA1 f.sub.3 (A)-.gamma..sub.A .ltoreq..DELTA.f.sub.3 max.ltoreq.f.sub.3 (A)+.gamma..sub.A'. . . for checking thickness
where .alpha..sub.A, .alpha..sub.A', .beta..sub.A, .beta..sub.A', .gamma..sub.A, .gamma..sub.A, are constants to identify the inserted coin as an A coin if the maximum frequency changes of the inserted coin hold this relationship with the reference values thereof.
These constants are generally determined accumulatively according to the variations of the A coin, change in ambient temperature and secular variations of the component parts of the apparatus. The apparatus is so constructed that the A coin is rightly identified even when these factors change at the same time. If the performance to eliminate spurious coins is to be improved, however, these constants should be as small as possible. Nevertheless, a small value of a constant poses the problem that an actually-inserted A coin may not be identified under variations of the coin, changes in the ambient temperature or secular variations of the component parts of the apparatus, while if these constants are large, a spurious coin that may be inserted is likely to be identified as an A coin. In these days in which coins of high denominations are widely used, the cry or demand is especially high for an improved performance to eliminate spurious coins.